A. Technical Field
The present invention relates to a water-swellable crosslinked polymer composition and its production process, more specifically, a water-swellable crosslinked polymer composition and its production process wherein the water-swellable crosslinked polymer composition comprises an anionic crosslinked polymer and a cationic crosslinked polymer and has a bulk density in a specific range. The present invention further relates to a water-swellable crosslinked polymer and its production process wherein the water-swellable crosslinked polymer is to easily give the above water-swellable crosslinked polymer composition. The present invention still further relates to uses of the above water-swellable crosslinked polymer composition.
B. Background Art
In recent years, synthetic water-absorbing materials, which are called water-absorbent resins, have been developed and are being put to practical use not only as constituent materials of sanitary materials such as sanitary napkins and disposable diapers, but also for purposes which need the water-absorbent resin, for example, industrial purposes such as sealing materials, dewfall-preventive materials, freshness-keeping materials, and solvent-dehydrating materials, and water-holding purposes in such as tree planting, agriculture, and horticulture.
As to the above water-absorbent resin, many ones as obtained by giving a crosslinked structure to hydrophilic high-molecular compounds are known, and examples thereof include: partially-neutralized and crosslinked poly(acrylic acids); hydrolyzed graft polymers of starch-acrylonitrile; neutralized graft polymers of starch-acrylic acid; saponified copolymers of vinyl acetate-acrylic acid ester; hydrolyzed copolymers of acrylonitrile or acrylamide, or crosslinked polymers of these hydrolyzed copolymers; and crosslinked polymers of polyethylenimine.
Furthermore, WO 92/20735 discloses a technical fundamental conception about absorption of electrolyte solutions by combinations of polymer particles having two different ions and exhibiting the ion exchangeability, and examples of application of this technique are disclosed in JP-A-081468/1992, WO 98/24382, WO 98/37149, and WO 99/25393. These techniques are, for example, such that an anionic water-swellable crosslinked polymer particle is combined with a cationic water-swellable crosslinked polymer particle to form a neutralized structure from an acid group of the former polymer particle and a basic group of the latter polymer particle by the salts which absorbing solutions contain, with the result that each of these polymer particles becomes so water-swellable that the combination of these polymer particles can exhibit more excellent swellability than conventional neutralized water-absorbent resins, and further can also take electrolytes (which are problems to the conventional neutralized water-absorbent resins) in to prevent the salt effect and, as a result, can enhance the ability to absorb the electrolyte solutions much more than conventional cases.
However, the above WO 92/20735, WO 98/24382, and WO 98/37149 merely disclose technical fundamental conceptions about combinations of polymer particles, and never consider absorption properties in practical use. In addition, WO 99/25393 proposes forming a microdomain in the polymer particles for the purpose of improving the absorption properties, but this case is found to contrarily deteriorate the desalting effect. The efficiency in the use of water-absorbing materials is important particularly for practical use of such as disposable diapers, therefore the diffusibility of liquids and further the properties of absorbing the electrolyte solution are more important; nevertheless this respect is not taken into consideration in the above prior arts at all. Thus, in the case where the above prior arts are intactly applied to such as disposable diapers, there are problems in respect to such as absorption rate, absorption capacity, and liquid permeability, therefore a satisfactory product is not obtained.
A. Objects of the Invention
An object of the present invention is to provide a water-swellable crosslinked polymer composition and its production process wherein the water-swellable crosslinked polymer composition comprises an anionic crosslinked polymer and a cationic crosslinked polymer, and is excellent in the desalting property and further in the absorption properties under load, and is therefore highly practicable. Another object of the present invention is to provide: a water-swellable crosslinked polymer and its production process wherein the water-swellable crosslinked polymer is to easily give the above water-swellable crosslinked polymer composition; and further, uses of the above water-swellable crosslinked polymer composition.
B. Disclosure of the Invention
In order to solve the above problems, the present invention provides the following:
(1) A water-swellable crosslinked polymer composition, which is particulate and comprises an anionic crosslinked polymer and a cationic crosslinked polymer, with the water-swellable crosslinked polymer composition being characterized by having a bulk density of not more than 0.5 g/ml.
(2) A water-swellable crosslinked polymer composition, which is particulate and comprises an anionic crosslinked polymer and a cationic crosslinked polymer, with the water-swellable crosslinked polymer composition being characterized in that at least either one of the anionic crosslinked polymer and the cationic crosslinked polymer has a bulk density of not more than 0.5 g/ml.
(3) A particulate cationic crosslinked polymer, which has a bulk density of not more than 0.5 g/ml and exhibits an absorption capacity of at least 5 g/g for physiological saline solution without load.
(4) A production process for a water-swellable crosslinked polymer, which comprises the step of carrying out a crosslinking reaction of a solution under bubbles-containing conditions wherein the solution contains at least a water-soluble polymer and a crosslinking agent.
(5) A production process for a water-swellable crosslinked polymer composition, which comprises the steps of: carrying out a crosslinking reaction of a solution under bubbles-containing conditions to obtain a cationic crosslinked polymer wherein the solution contains at least a polyamine and a crosslinking agent; and then mixing the resultant cationic crosslinked polymer and an anionic crosslinked polymer together.
(6) An absorbent articles, which comprises an absorbent layer, a sheet with liquid permeability, and a sheet with liquid impermeability, wherein the absorbent layer contains the above water-swellable crosslinked polymer composition according to the present invention, and is interposed between the sheet with liquid permeability and the sheet with liquid impermeability.
These and other objects and the advantages of the present invention will be more fully apparent from the following detailed disclosure.